Transfer switch for a xerographic apparatus



Feb. 14, 1967 J. J. SCHOEN ET AL 3,304,476

TRANSFER SWITCH FOR A XEROGRAPHIC APPARATUS Filed April 30, 1964 2 Sheets-Sheet 1 2 N 8 r\ 2 o INVENTORS.

JOHN J. SCHOEN ATTORNEYS Feb. 14, 1967 SCHOEN ET AL TRANSFER SWITCH FOR A XEROGRAPHIC APPARATUS Filed April 30, 1964 2 Sheets-Sheet 2 FIG.2

FIG.3

INVENTORS. JOHN J. SCHOEN JOSE STONE ATTO/P/VEVS United States Patent f 3,304,476 TRANSFER SWITCH FOR A XERGGRAPHHI APPARATUd John J. Schoen, Rochester, and loseph lit. Stone, Penfieid,

N.Y., assignors to Xerox Qorporation, Rochester, ELY,

a corporation of New York Filed Apr. 30, 1964, Ser. No. 363,880 2 Claims. ((31. 317-262) This invention relates to the field of xerography, and particularly to an improvement in a switch mechanism and circuit therefor for selectively placing a positive or negative electrostatic charge relative to a xerographic plate by a corona discharge device.

In the process of xerography, for example, as disclosed in the Carlson Patent 2,357,809, a xerographic plate,

comprisin a layer of photoconductive insulating material on a conductive backing, is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the radiation intensity which reaches them and thereby creates an electrostatic latent image on or in the plate coating.

Development of the image is effected with developer material which comprises in general a mixture of suitable pigmented or dyed electroscopic powder, called toner. In the development of the image, the toner powder is brought into contact with the plate and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. Thereafter, the developed xerographic image is transferred to a support or transfer material to which it may be fixed by any suitable means.

In general, corona charging may be accomplished in a variety of ways, but generally the corona discharge device may comprise a single wire or series of parallel wires that are electrically energized from a high voltage source relative to the plate which may be moved at a uniform rate of speed to place an electrostatic charge thereon. Conversely, the plate may be held stationary and the corona discharge device may be moved relative to it to deposit a charge thereon.

After development of the electrostatic latent image upon the xerographic plate, transferring the image is accomplished by laying a piece of paper over the electrostatic charge pattern that has been developed and applying a uniform electrostatic charge over the back surface of the paper, such charge being of a polarity to attract the powder image to the paper and then separating the paper from the plate surface. In the process of being electrostatically attracted to the adjacent surface of the paper, a portion of the developing powder comprising the original powder image adheres to this surface of the paper and forms a readily readable image thereon. The polarity of the electrostatic charge that is utilized for attracting the toner powder to the sheet of paper from the xerographic plate is of opposite polarity to that polarity which was used to attract the powder to the xerographic plate during development of the latent image. After the toner powder has been attracted to the sheet of paper and the sheet has been removed, another corona discharge device is applied to the xerographic plate for releasing or cleaning therefrom any residual charge that may remain thereon after the transferring process in order to recondition the plate for reuse. Generally, there are provided two corona discharge devices, one to effect transfer of the toner particles to the sheet of paper and a second device for releasing or cleaning the xerographic plate of any residual charge thereon.

In the present invention, a single corona discharge 3,304,476 Patented Feb. 14, 1&5?

electrode is employed and a reversing switch is provided in the electrical circuit for the corona discharge device which will permit energization of the corona discharge device with either high positive voltage or high negative voltage. This switching mechanism is particularly constructed and arranged to avoid arcing of the electrical contacts that are provided with the switching mechanism.

The principal object of the present invention is to improve the construction -of a corona discharge electrode control circuit for use in xerographic systems.

A further object is to prevent arcing of the contacts in a reversing transfer switching mechanism. A further object of the invention is to produce positive or negative corona for xerographic processing utilizing a reversing transfer switch which is compact, of low cost manufacture, and requires a minimum of maintenance.

Briefly, these and other objects of the invention are attained by the use of a power supply circuit having a three-pole switch mechanism which will selectively conduct positive or negative current to a single corona discharge device. The switching mechanism is provided with a specially contoured single piece switch element which is movable between the various electrical contacts in the switch without producing arcing between the contacts or between the contacts and the switch element.

For a better understanding of the invention, as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings, wherein:

FIG. 1 is an isometric view of a xerographic plate transfer apparatus employing the present invention;

FIG. 2 is a plan view of a switching mechanism of the present invention shown partly broken away; and,

FIG. 3 is a cross section of the switching mechanism taken along the line 33 of FIG. 2.

The device shown in FIG. 1 is particularly adapted for utilizing the present invention and comprises a main frame 10 which supports a pair of plate guides 12 and a pair of corotron tracks 14. A xerographic plate 16 is positioned within the frame 10 on the plate guides 12 and has a photoconductive surface 18 on the top surface thereof. Prior to use of this apparatus, the xerographic plate has been charged, exposed, and developed in a xerographic camera of the type disclosed in copending application Serial No. 348,950, filed in the name of Norbett H. Kaupp et al., and has thereon a powder image of an original copy that is to be reproduced. An electrostatic transfer device 26 is suitably supported above the xerographic plate and is movable along the frame 10 over the length of the xerographic plate.

A sheet of support material 22, adapted to receive a powder image of the copy being reproduced, is fed through the electrostatic transfer device by means of a pair of resilient drive rollers 24 mounted on a shaft journaled in the side frames 26 and 28 of the transfer device. A pinion 38 mounted on each end of the transfer device mesh with the corotron tracks 14, shown herein as a pair of gear toothed racks. As the electrostatic transfer device 2h is moved along the length of the xerographic plate 16, the pinions 30 mesh with the teeth of the track 14 and rotate the resilient drive rollers 24. The linear movement of the drive rollers 24 is the same as the linear movement of the electrostatic transfer device 29 across the surface of the xerographic plate without any relative movement between the plate surface and the support material.

Within the cover housing 32 of the transfer device there is suitably mounted an electrostatic discharge device 34 consisting of a shield 36 around at least one wire 33 which gives off a corona discharge when a high potential is applied thereto. I The corona discharge is effective to place a positive or negative electrostatic charge on the back surface of the sheet of support material 22 as the corotron is moved over the surface of the xerographic plate. The electrostatic discharge from the corotron effectively tacks the sheet of support material 22 to the plate surface and prevents relative movement between the support material and the xerographic plate. When the electrostatic charge on the surface of the sheet of support material 22 is positive, as in conventional xerograp'hic development where a positive reproduction is to be produced from a negative latent image on the xerographic plate, the positive charge attracts the negatively charged powder image from the plate surface and causes it to adhere to the surface of the support material so that a powder copy of the image to be reproduced remains on the surface of the support material when the support material is removed from the surface of the xerographic plate. When the electrostatic charge is negative, which is useful for cleaning the residual image on the plate, the charge reduces the attraction between the toner and the plate making the residual image easier to wipe off.

A negative electrostatic charge on the wire 33 is also useful for producing negative reproductions which are accomplished by transferring on a sheet of support material an image developed with positively charged toner in the developer.

In order to selectively impress upon the wire 33 either the positive or negative charge, there is provided in the circuit for the transfer device a rotary reversal switch indicated by the reference numeral 40 in FIG. 1, and illustrated in detail in FIGS. 2 and 3. The switch 4-0 is particularly arranged and constructed in order to minimize arcing that may occur during switching thereof of the relatively high voltage involved for xerogr-aphic processmg.

As shown in FIGS. 2 and 3, the switch 40 comprises a circular housing 42, preferably made of insulating material such as Lucite, having a cup-shaped lower portion 44 and a cap 46 adapted to cover the portion 44. The portion 44 is formed with a circular rim 4% having an inner surface 49 with a diameter equal to the outer diameter of the cooperating section of the cap 46 which, when assembled, fits tightly within the rim 4S. Projecting through the switch housing along the axis thereof is a drive shaft 50 which is mounted for rotation through apertures 52, 54, formed in the cover cap 46 and the portion 4-4, respectively. A suitable knob is secured to the shaft for facilitating manual actuation of the switch to either of its control positions. Within the housing, and secured to the shafts 50, is a flat rectangular switch element 56, made from insulating material such as Lucite, having the thickness slightly less than the spacing between the opposed adjacent surfaces of the portion 44 and cap 46 for permitting movement therebetween.

The switch element 56 is secured to the shaft at one end and, upon rotation of the shaft, the opposite end 58 of the element is movable in an arcuate path within the housing. Rotation of the element 56 and arcuate move ment of the end 58 is limited by a pair of stops 6% secured to the portion 44 on either side of the aperture 54 and the shaft 50. As shown in FIG. 2, the element 56 is in one of its positions of control as limited by the righthand stop 60. The left-hand stop 60 will determine the other position of control for the element 54 which is thereby adapted for 90 of rotation between its two con- :trol positions.

At the extreme outer surface of the end 58 of the switch element, there is mounted a curved metallic conductor bar 62 which is secured to the end 58 by a pair of screws 64. The bar is adapted to slidably engage the inner surface 49 of the rim 48 when the switch element is rotated by the shaft 50. In order to provide good electrical conduction through the bar 62 it is preferred that the bar be resilient 3 nd flexed when assembled in the housing 42 in order to insure that the bar is resiliently biased against the inner surface 40 of the rim 48.

The conductor bar 62 is of sufficient length and curved in a manner such that at two points, 68 and 70, on the bar, contact is made with the inner surface 49 at corresponding points thereon that subtend an angle of 90 about the axis of the shaft 50. Located at three positions on the rim 4t) and projecting radially therethrough are three contact elements 72, 741, 76, each of which extends slightly radially inwardly of the surface 49. These contact elements may be secured to the rim by any suitable means and are located at positions which are spaced 90 from each other. In this manner, the conductor bar 62 is adapted to bridge across and engage any two adjacent contacts for each of its two control positions. For example, as shown in FIG. 2, the bar 62 is in engagement with the contact elements 74 and 76 since the curved points 68, 70, of the bar are resiliently held in contact with the elements, respectively.

During actuation of the switch 40 from a first of its control positions to its second position by rotation of the shaft 50, the switch element 56 will be moved from the position shown in FIG. 3 to a position corresponding thereto on the other side of the housing 42. In the first control position, the bar 62 connects the contact elements 74 and '76, and in the second position, the bar connects the elements '72 and 74. In either position, the contact element 74 is utilized, therefore, as the contact for connection to transfer device 20 in the electrical circuit that utilizes the switch.

In order to lock the shaft 50 into either of its two controlling positions, there is provided a detent mechanism which comprises a disc 80 secured at its center point to the end of the shaft and rotatable therewith, and a spring biased latch member 82. in the form of a small roller which is adapted to ride into notches M formed in the periphery of the disc 80. The roller 82 is mounted for rotation at one end of a leaf spring 86- pivotally mounted at its other end to a plate 88 upon which is secured a single-pole, single-throw microswitch 90. The leaf spring 86 is adapted to actuate the microswitch, upon fiexure thereof, between the open and closed positions of the switch.

The actuation of the switch 9'0 is such that when the rolier 8,2 is in one of the notches 84, the switch is closed and, when the roller is rolled out of a notch by rotation of the disc 80, the switch will be actuated to its closed position. It will be apparent that the cooperative action of the roller and notches serves to releasably lock the shaft 50 in each of its two controlling positions, previously described. The notches 84 are spaced 90 from each other and are positioned so that the roller is in one of the notches for each control position of the switch 40. It will be noted that the curved positions of the bar 62 adjacent points 68, 70, are such that the switch element 56 can be rotated a few degrees without actually disengaging from the contacts 72, 74, 76. This limited rotation allows the roller 82 to be completely moved out of the notches and onto the periphery of the disc 80 to actuate the microswitch to an open position before the bar is removed from the contacts.

In FIG. 1, the reversal switch 40 and the microswitch 90 are shown in an electrical arrangement for controlling the corona discharge on the wire 38 in the transfer device 20. Electrical power for the transfer device may be taken from a conventional volt A.C. source and is conducted to a DC. power supply PS-l which converts the A.C. power to direct current suitable for producing corona discharge in a xerographic processing apparatus. The DC. level for this use is on the order of 6,000 to 7,000 volts and care must be taken in order to prevent arcing of contacts of switches that are used in controlling this high voltage power.

From the DC. power supply PSl, positive voltage is conducted to the contact 72 of the transfer switch 40 by way of a conductor 104, and negative voltage is conducted through a conductor 1% to the contact 76. For energizing the corona discharge wire 33, the common contact 74 is connected to the wire 38 by way of a conductor 108. To complete the circuit for producing corona, the microswitch 90 is connected in the conductor 102 between the D.C. supply PS-l and the AC. source.

In operation, with the conductor bar 62 bridged between the contacts 72 and 74, positive voltage is conducted to the discharge wire 38 by the conductor T08 and, since the detent roller 82 is in one of the notches 84, the switch 90 is in closed condition to permit electrical conduction to the D.C. power supply PS-l. With a positive potential of approximately 6,0007,000 volts on the wire 38, the corona discharge resulting from the wire is suitable for transferring Xerographic toner particles from the xerographic plate 16 to the sheet of material 22 in order to present a posi tive representation of the developed image on the plate 16. In the event that a negative image is desirable or that, after transfer of an image, the plate 16 requires cleaning of the residual charge wherein it is necessary that a negative charge be placed upon the wire 38, the shaft 50 is rotated 90 in a clockwise direction, as shown in FIG. 2. This rotation will effect arcuate movement of the conductor bar 62 to a position which will bridge across the contacts 74 and 76. In this condition, the discharge wire 38 will be energized with approximately 6,0007,000 volts of negative voltage.

The opening and closing of the microswitch 90 is arranged so that the switch 90 will be opened to terminate electrical conduction to the supply PS1 before the conductor bar 62 is moved to either bridge, or unbridge its engagement with the contacts 72, 74, or 74, 76, as the case may be. With this arrangement, there is no current on the contacts as the bar 62 is moved away or toward them during actuation of the reversal switch into any of its controlling conditions. In this manner, arcing at the contacts, which experience relatively high voltages, is eliminated.

While the present invention as to its objects and advantages, as described herein, has been carried out in one specific embodiment thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the scope of the appended claims.

What is claimed is:

1. A charging circuit for applying positive or negative electrostatic charge selectively to a Xerographic plate including:

a corona charging device having at least one corona discharge electrode movable relative to and adjacent a xerographic plate;

D.C. power supply connected to a source of electric current having positive and negative output terminals and a circuit connected to said electrode for conducting a D.C. potential thereto and thereby produce a corona discharge;

said circuit including a switch mechanism having a first contact connected to said positive terminal, a

second contact connected to said negative terminal,

and a third contact connected to said electrode;

said switch mechanism having a rotatable conductive eiement movable to a first position to bridge across said first and third contacts to permit energization of said electrode with positive voltage and movable to a second position to bridge across said second and third contacts to permit energization of the electrode with negative voltage;

means for selectively actuating said conductive element to either of said positions; and,

a switching device for opening the circuit to said power supply from said source for terminating conduction thereto before said conductive element is moved into on out of engagement with said contacts.

2. A charging circuit for applying positive or negative electrostatic charge selectively to a Xerographic plate including:

a corona charging device having at least one corona discharge electrode movable relative to and adjacent a Xerographic plate;

a D.C. power supply connected to a source of electric current having positive and negative output terminals and a circuit connected to said electrode for conducting a D.C. potential thereto to thereby produce a corona discharge;

said circuit including a switch mechanism having a first contact connected to said positive terminal, a second contact connected to said negative terminal, and a third contact connected to said electrode;

said switch mechanism having a rotatable conductive element movable to a first position to bridge across said first and third contacts to permit energization of said electrode with positive voltage and movable to a second position to bridge across said second and third contacts to permit energization of the electrode with negative voltage;

a manually actuatable shaft connected to said conductive element for selectively actuating the same to either of said positions;

detent means operatively connected to said shaft for releasably locking said shaft and therefore said conductive element in either of said positions when the shaft has been actuated to either of said positions; and, switch device electrically connected in the circuit between the source and the power supply and having a circuit opening and closing actuating member operatively associated with the detent means;

said switch device being actuatable to an open condition or said detent means is actuated to release its hold upon the shaft and before the conductive element is moved out of either of said positions.

References Cited by the Examiner UNITED STATES PATENTS 2,790,082 4/1957 Gundlach 250-495 2,856,533 10/1958 Rosenthal 250-49.5 2,890,343 6/1959 Bolton 250-495 3,240,596 3/1966 Mediey et a1 961 MILTON O. HIRSHFIELD, Primary Examiner. J. A. SILVERMAN, Assistant Examiner. 

1. A CHARGING CIRCUIT FOR APPLYING POSITIVE OR NEGATIVE ELECTROSTATIC CHARGE SELECTIVELY TO A XEROGRAPHIC PLATE INCLUDING: A CORONA CHARGING DEVICE HAVING AT LEAST ONE CORONA DISCHARGE ELECTRODE MOVABLE RELATIVE TO AND ADJACENT A XEROGRAPHIC PLATE; A D.C. POWER SUPPLY CONNECTED TO A SOURCE OF ELECTRIC CURRENT HAVING POSITIVE AND NEGATIVE OUTPUT TERMINALS AND A CIRCUIT CONNECTED TO SAID ELECTRODE FOR CONDUCTING A D.C. POTENTIAL THERETO AND THEREBY PRODUCE A CORONA DISCHARGE; SAID CIRCUIT INCLUDING A SWITCH MECHANISM HAVING A FIRST CONTACT CONNECTED TO SAID POSITIVE TERMINAL, A SECOND CONTACT CONNECTED TO SAID NEGATIVE TERMINAL, AND A THIRD CONTACT CONNECTED TO SAID ELECTRODE; SAID SWITCH MECHANISM HAVING A ROTATABLE CONDUCTIVE ELEMENT MOVABLE TO A FIRST POSITION TO BRIDGE ACROSS SAID FIRST AND THIRD CONTACTS TO PERMIT ENERGIZATION OF SAID ELECTRODE WITH POSITIVE VOLTAGE AND MOVABLE TO A SECOND POSITION TO BRIDGE ACROSS SAID SECOND AND THIRD CONTACTS TO PERMIT ENERGIZATION OF THE ELECTRODE WITH NEGATIVE VOLTAGE; MEANS FOR SELECTIVELY ACTUATING SAID CONDUCTIVE ELEMENT TO EITHER OF SAID POSITIONS; AND, A SWITCHING DEVICE FOR OPENING THE CIRCUIT TO SAID POWER SUPPLY FROM SAID SOURCE FOR TERMINATING CONDUCTION THERETO BEFORE SAID CONDUCTIVE ELEMENT IS MOVED INTO ON OUT OF ENGAGEMENT WITH SAID CONTACTS. 